Human powered vehicles suffer from the limited output power available from the human limbs. A typical healthy adult human is capable of producing about 100 to about 150 watts for periods of an hour or more. Trained athletes are capable of producing about 250 watts (0.15 horsepower) for long periods and about 750 watts (1 horsepower) for short periods. An adult human in poor condition is capable of producing only about 50 watts.
For convenience in the following description, the term bicyclist will be used in a general sense to refer to any human powered activity in which a vehicle is driven by human muscle power. Besides bicycles and tricycles, this can also include rowed boats and human-powered aircraft.
For comfortable pedaling of a bicycle or tricycle over a substantial period of time, a sustainable power output must be maintained. Power output is related to pedal force and pedal cadence (number of pedal strokes per minute). A suitable balance between pedal force and cadence is required. If the pedal force applied is too high, the legs of the pedaler become tired quickly. If the pedaling cadence is too high, the pedaler runs out of breath in a short time. Accommodation to the required compromise of power output, pedal force and cadence is found on most touring bicycles and tricycles in the form of a gearshift mechanism. The gearshift mechanism, either internal to the driven wheel (for example, a Sturmy Archer type) or in the drive train from the pedal crank to the driven wheel (for example, the derailleur type), varies the distance of forward travel achieved for each rotation of the pedal crank. The number of rotations of the driven wheel per rotation of the pedal crank is known as the inverse gear ratio.
The strategy adopted by most bicyclists for maintaining the desired balance basically consists of applying a comfortable pedal force and adjusting the gear ratio until an approximation of a target cadence is attained. That is, the bicyclist selects a gear, continues to apply a comfortable pedal force, and determines whether a desirable range of cadence results. If the resulting cadence is too high, the bicyclist shifts gears to select a higher gear ratio--if it too low, the bicyclist selects a lower gear ratio.
For a given speed, the power output is that required to balance the following factors:
rolling friction with the road, PA1 drive train friction, PA1 wind drag, PA1 slope of road, PA1 weight of rider
Of these factors, rolling friction and drive train losses are substantially constant. In normal bicycle operation, wind drag is a significant variable because headwind and tailwind add or subtract from the relative wind produced by vehicle motion. The dominating variables, though, are slope and the weight of vehicle and rider, since an up slope requires the raising of the vehicle and rider from the lowest to the highest point on the slope.
In my prior U. S. Pat. No. 4,552,088, I disclose an inclinometer in which the up-slope angle of the road being traveled is calibrated in terms of the gear of a 10-speed bicycle which should be selected. Tests reported in this patent show that, for moderate pedaling with a 10-speed bicycle, a suitable cadence of about 55 strokes per minute could be maintained to an up-slope angle of about 1.8 degrees with very light pedal pressure. At this up-slope, the gearshift has reached the lowest gear at which the inverse gear ratio (the number of rear-wheel rotations per rotation of the drive sprocket) is about 1.75. At greater up slopes, some combination of additional pedal force and reduced cadence must be sustained in order to maintain headway. This disclosure uses headwind speed as a parameter. This patent discloses the use of a pendant weight driving a variable resistor to produce an electrical signal responsive to slope. The slope signal is used to produce a slope indication on a slope meter which guide the selection of a gear. Disturbances in the output signal due to road irregularities and pedal acceleration pulses are treated as noise, and are filtered out, either electrically or mechanically.
My prior patent, and the remainder of the prior art is silent about a solution, except for motor drive, when the slope increases to a value at which the bicyclist is using the lowest possible gear, the cadence has slowed to a very low value, and the muscle power produced by the bicyclist cannot be increased sufficiently to maintain a target cadence, or even to continue riding (the picture of a bicyclist off the bicycle, pushing the vehicle up a hill, is all too common).
My prior U.S. Pat. No. 4,526,036 discloses a technique for detecting a pedaling cadence of a bicycle. A lightly restrained weight, rotatable about a vertical axis, is displaced forward and backward by accelerations and decelerations of successive pedal pulses. An electronic circuit provides an indication of the cadence for the guidance of the bicycle rider.
My prior U.S. Pat. No. 4,423,630 discloses a cyclic power monitor which uses a pressure sensor on one pedal of a bicycle. The measured pedal force, together with the pedaling cadence detected from variations in the pedal force applied to the pressure sensor, drive indicators indicating cadence, pedal force, and power output. Slope is not derived in this disclosure.
Auxiliary power for bicycles has been a consistent aim to enable comfortable bicycle travel, including travel routes containing uphill portions too steep for traverse at a comfortable power output level. This aim has been thwarted by the noise and pollution of small attachable fossil-fueled motors, and by the limited power storage capacity of batteries.
A battery assist for a bicycle commonly consists of a small electric motor controlled by an ON-OFF switch. This device has two main drawbacks. First, a bicycle rider tends to turn on the battery assist during times that it is not needed, thereby reducing battery endurance. Secondly, this device permits addition of auxiliary power during downhill travel. Auxiliary power during downhill travel is well-known to drive a bicycle to dangerously high speeds.
It would be convenient, but presently unattainable in a convenient manner, to measure the output power actually produced, and then to add auxiliary power only when the rider's output exceeds a preset comfortable output power. In this manner, the rider output power would remain the principal power source for the vehicle, but the exertion would remain within a range which would permit long rider endurance, but would use only the minimum amount of stored battery energy actually required for this augmentation.
Several practical difficulties have so far prevented the introduction of such a system. Of particular difficulty is the measurement of pedal force exerted on a relatively moving pedal, and the generation and application of auxiliary power at a relatively non-moving part of the bicycle.